1. Field of the Invention
This invention generally relates to an impact-absorbing shock absorber with two telescoping tubes, in particular for motor vehicles, to decelerate the vehicle by hydraulic damping forces and pneumatic spring forces when the vehicle collides with an obstacle. Such an impact absorber can typically have an inner tube closed by a bottom, a gas chamber adjacent to the bottom and containing a gas cushion at high pressure, a separating piston guided so that it slides in a sealed manner inside the inner tube, a first fluid chamber, a partition fastened in the inner tube and provided with throttle openings, and a second fluid chamber which is connected by means of the partition to the first fluid chamber.
2. Background Information
German Patent No. 24 04 706 discloses a hydropneumatic impact-absorbing shock absorber in which an inner tube can be pushed into an outer tube in the event of a collision. The inner tube has a gas chamber which contains a gas cushion, which gas chamber is separated by a separating piston from a first fluid chamber. The first fluid chamber is in turn delimited on the end of the inner tube by a partition which has a throttle hole. In this manner, a connection can be formed between the first fluid chamber in the inner tube and a second fluid chamber which is formed by the outer tube. The impact-absorbing shock absorber has connection elements on the inner tube and on the outer tube for connecting the inner tube and outer tube relative to one another on respective ones of the vehicle body and a bumper.
In the event of a collision, the inner tube is pushed into the outer tube, and thereby displaces damping fluid out of the second fluid chamber, through the throttle opening of the partition, and into the first fluid chamber in the inner tube. During this process, a damping force is generated. The increase in the volume of the first fluid chamber is compensated by the movement of the separating piston. A purely hydraulic damping occurs, but it is only suitable for absorbing forces generated during collision at speed of up to about 4-8 kilometers per hour (km/h). Above this energy absorption threshold, the bumper or the body parts connected to the impact-absorbing shock absorber can be permanently deformed.
German Patent No. 34 19 165, which corresponds to U.S. Pat. No. 4,641,872, discloses an impact-absorbing shock Absorber which, in addition to a hydraulic damping, has a deformation shock absorber in the form of a folding tube. As soon as the energy absorption threshold for the hydraulic damping is exceeded, there is a deformation of the deformation tube up to an energy absorption threshold of approximately 15 km/h. But this arrangement has a serious disadvantage, since after a collision, as a result of a deformation of the folding tube, there can be a permanent change, or shortening, in the length of the impact-absorbing shock absorber. Moreover, an impact-absorbing bumper of this type has the disadvantage that all the large components, i.e. the first fluid chamber, the second fluid chamber and the gas chamber, are arranged in a row, and are, in turn, axially disposed adjacent to the space for the deformation tube.
Precisely the same disadvantages are essentially exhibited by the impact-absorbing bumper which is disclosed in European Patent Application EP-A 0 473 955. In this known impact-absorbing shock absorber, a deformation piston is pushed inside a deformation tube, whereby the deformation piston is connected to the hydraulic damping apparatus by means of a piston rod. In addition to the above-mentioned disadvantages, the interposition of a piston rod between the hydraulic damping apparatus and the deformation piston has the disadvantage that the piston rod has elasticities, so that the damping force has a maximum as a function of the distance, which is difficult to determine. In other words, it is generally impossible to rule out the possibility that the vehicle body will begin to deform before the beginning of the deformation of the deformation body on the impact-absorbing shock absorber.